Pressure-sensitive or heat-sensitive recording papers rely on two components to form color. One component is a colorless or slightly colored dyestuff or color precursor. The other component is an acidic material or color developer. which is capable of forming a color by reaction with the dyestuff or color precursor. Marking of the recording papers is effected by pressure or heat which transfers one reactant to the other.
Pressure-sensitive recording material consists, for example, of at least one pair of sheets which contain at least one dyestuff or color precursor, dissolved in an organic solvent, and a color developer. The dyestuff or color precursor effects a colored marking at those points where it comes into contact with the color developer.
In order to prevent the color precursors contained in the pressure-sensitive recording material from becoming active prematurely, they are usually separated from the developer. This can advantageously be accomplished by incorporating the color precursors in foam-like, sponge-like, or honeycomb-like structures. Preferably, the color formers are enclosed in microcapsules which usually can be ruptured by pressure.
In a common method of manufacture of pressure-sensitive recording papers, better known as carbonless copy papers, a layer of pressure-rupturable microcapsules containing a solution of colorless or slightly colored dyestuff or color precursor, is normally coated on the backside of the front sheet of paper of a carbonless copy paper set. This coated backside is known as the CB coating. In order to develop an image or copy, the CB coating must be mated with a paper containing a coating of suitable color developer on its front. This coated front color developer coating is called the CF coating. Marking of the pressure-sensitive recording papers is effecting by rupturing the capsules in the CB coating by means of pressure to cause the dyestuff precursor solution to be exuded onto the front of the mated sheet below it. The colorless or slightly colored dyestuff, or dyestuff precursor, then reacts with the color developer in the areas at which the pressure was applied, thereby affecting the colored marking. Such mechanism or the producing technique of pressure-sensitive recording papers is well known.
Various developers for use in thermoreactive recording material are also well known. Thermoreactive recording material usually contains at least one carrier, one color precursor, one solid developer and, optionally, also a binder. The thermoreactive recording system comprise, for example, heat-sensitive recording and copying materials and papers. These sytems are used, for example, for recording information, e.g., in electronic computers, teleprinters or telewriters, or in recording and measuring instruments. The image (mark) formation can also be effected manually with a heated pen. Laser beams can also be used to produce heat-induced marks. The thermoreactive recording material can be so composed that the color precursor is dispersed or dissolved in one binder layer and the developer is dissolved or dispersed in the binder in a second layer. Another possibility consists in dispersing both the color precursor and the developer in one layer. By means of heat, the binder is softened at specific areas and the color precursor comes into contact with the developer at those points where heat is applied and the desired color develops at once.
Color precursors are well known to those experienced in the field and any such color former may be used in conjunction with the present invention, e.g., those belonging to the classes of the phthalides, fluoranes, spiropyranes, azomethines, triarylmethane-leuco dyes, of the substituted phenoxazines or phenothiazines, and of the chromeno or chromane color formers. Examples of such suitable color precursors are: crystal violet lactone, 3,3-(bisamino-phenyl)-phthalides, 3,3-(bisubstituted indolyl)-phthalides, 3-(aminophenyl)-3-indoylphthalides, 6-diaalkylamino-2-n-octylaminofluoranes, 6-dialkylamino-2-arylaminofluoranes, 6-dialkylamino-3-methyl-2-arylaminofluoranes, 6-dialkylamino-2- or 3-lower alkylfluoranes, 6-dialkylamino-2-dibenzylaminofluoranes, 6-dialkylamino-2-dibenzylaminofluoranes, 6-diethylamino-1,3-dimethylfluoranes, the lactonexanthenes, the leucoauramines, the 2-(omega substituted vinylene)-3,3,-disubstituted-3-1-1-indoles, 1,3,3-trialkylindolinospirans, bis-(aminophenyl)-furyl-, phenyl- or carbazolylmethanes, or benzoyl-leucomethylene blue.
Known color developers for use in such pressure-sensitive or heat-sensitive recording papers have included:
(1) novolac phenolic resins made by acid catalyzed condensation of phenol, resorcinol, pyrogallol, cresols, xylenols, or alkyl phenols, such as p-tertiary butyl phenol, with aldehydes such as formaldehyde, acetaldehyde, benzaldehyde, and butyraldehyde;
(2) Metal salts of aromatic carboxylic acids with an OH group at the ortho position, such as zinc salt of salicylic acid, 3,5-di-tert-butyl salicylic acid, octyl salicylic acid, and 1-hydroxy-2-naphthoic acid, and
(3) acid-treated clays such a kaolinites and attapulgites.
The search has continued for other developers having high developing power, rapid developing speed, good light resistance and time stability. Examples of some colored developers which have been developed in the past which are somewhat related to those of the present invention are disclosed in U.S. Pat. No. 4,291,901 to Petitpierre and Japanese patent disclosure No. 1979-111905.